Abstract
MicroRNAs (miRNAs) control expression of endogenous target genes through transcript cleavage or translational inhibition. Legume plants can form a specialized organ, the nodule, through interaction with nitrogen fixing soil bacteria. To understand the regulatory roles of miRNAs in the nodulation process, we functionally validated gma-miR171o and gma-miR171q and their target genes in soybean. These two miRNA sequences are identical in sequence but their miRNA genes are divergent and show unique, tissue-specific expression patterns. The expression levels of the two miRNAs are negatively correlated with that of their target genes. Ectopic expression of these miRNAs in transgenic hairy roots resulted in a significant reduction in nodule formation. Both gma-miR171o and gma-miR171q target members of the GRAS transcription factor superfamily, namely GmSCL-6 and GmNSP2. Transient interaction of miRNAs and their target genes in tobacco cells further confirmed their cleavage activity. The results suggest that gma-miR171o and gma-miR171q regulate GmSCL-6 and GmNSP2, which in turn, influence expression of the Nodule inception (NIN), Early Nodulin 40 (ENOD40), and Ethylene Response Factor Required for Nodulation (ERN) genes during the Bradyrhizobium japonicum-soybean nodulation process. Collectively, our data suggest a role for two miRNAs, gma-miR171o and gma-miR171q, in regulating the spatial and temporal aspects of soybean nodulation.
Highlights
The agricultural and ecological success of legume species is largely due to their ability to form a mutualistic relationship with rhizobium bacteria
We reported that miR171 targets the Nodulation Signaling Pathway 2 (NSP2) gene in soybean based on Parallel Analysis of RNA Ends (PARE) data (Arikit et al, 2014; Yan et al, 2015)
It became of interest to us to explore the function of these identical miRNAs derived from distinct primary transcript sequences, especially since subsequent analysis showed that both are involved in the regulation of soybean nodulation
Summary
The agricultural and ecological success of legume species is largely due to their ability to form a mutualistic relationship with rhizobium bacteria This beneficial microbe–plant symbiosis results in the formation of a specialized organ, the root nodule, which rhizobium bacteria colonize resulting in the conversion of atmospheric N2 into NH3, a form of nitrogen that can be readily utilized by the plants. This biological nitrogen fixation (BNF) allows legume plants to thrive in N-deficient soils without the necessity of N fertilizer addition. It is known that regulation of symbiotic development requires the action of a variety of regulatory factors, including a number of microRNAs (miRNAs)
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